Compositions comprising immobilised cells having enzymatic activity are known, for example in European Patent No. 0089165 which discloses a composition wherein a coating comprising E. coli which is fixed by means of a cross-linked polymer is on an inert carrier. This composition is used to prepare L-aspartic acid. European Patent Application No. 0297912 also discloses a biologically active material which comprises a coated particle wherein the coating comprises a the biological material and a cross-linked polymer.